I'm teaching my horse to bow. How should I ask him [[signal]]?

[Howdy&Bwoo]

I'm going to attempt to teach my horse to bow. I need a signal to ask him to bow once we get the basics down. I don't want to aks him to bow and one day he confuses it with a different signal and start bowing at a show. What would be a good way to ask him to bow without him confussing it with me asking him to square or pivot or something. I don't want to screw up what we already know/learning.
So what would be a good signal to bow? Would a crop be a good signal like tapping one of his legs, so he knows the crop means bow since I never use it on a normal basis? Thanks!